A lower limit on the heat capacity of the neutron star core

Understand

We show that observations of the core temperature of transiently-accreting neutron stars combined with observations of an accretion outburst give a lower limit to the neutron star core heat capacity.

• For the neutron stars in the low mass X-ray binaries KS 1731-260, MXB 1659-29, and XTE J1701-462, we show that the lower limit is a factor of a few below the core heat capacity expected if neutrons and protons in the core are paired, so that electrons provide the dominant contribution to the heat capacity.
• This limit rules out a core dominated by a quark color-flavor-locked (CFL) phase, which would have a much lower heat capacity.
• Future observations of or limits on cooling during quiescence will further constrain the core heat capacity.